LLC single stage power factor correction converter

ABSTRACT

A single stage PFC LLC power converter is consist of two transformer, one forward transformer, one main transformer. The first winding of the forward transformer is connected with a capacitor in series then paralleled with another capacitor and this circuit is connected with the primary winding of the main transformer in series as primary load circuit in LLC power converter, the energy through the main transformer is transferred to the secondary circuit and the energy through the first winding of the forward transformer is transferred to the second winding of the forward transformer to correct the input current waveform.

BACKGROUND OF THE INVENTION

1. Technical Field

The disclosure relates to a power-factor-corrected converter, and more particularly to a power-factor-corrected LLC converter in single stage.

2. Prior Art

Generally, the most conventional circuit for a power factor correction(PFC) employ an inductor as an energy-storage element and employ a boost control topology for correcting power factor and transferring the energy to a DC to DC converter. Therefore the material of the core of the inductor should be taken into consideration in order to avoid large hysteresis loss caused by pulse current. In order to maintain the stability of the boost control topology, additional compensation capacitors and complicated control circuit including circuit element such as an analog multiplier, are required to achieve the power factor correction. Furthermore, in the above mentioned circuit, other circuit elements having functions of frequency jitter, quasi resonant or valley switching are also included in clock control signals in order to reduce the generation of electromagnetic interference (EMI). Furthermore, because the boost control topology is employed for power factor correction, the output voltage in the circuit will boosted to a higher voltage level such as 400V. Therefore, high voltage switching elements should be used in DC to DC converter.

SUMMARY OF THE INVENTION

The first objective of the present invention is to provide a LLC power supply that operates from AC line voltage having power factor correction and output isolation,

The second objective of this invention is to provide for one stage power factor power correction in an AC to DC (LLC) converter.

The third objective of the present invention is to provide a more efficient PFC power supply circuit.

The fourth objective of the present invention is to provide a simple PFC power supply circuit to reduce manufacture cost.

Further objectives and advantage of this invention will be apparent from the following detailed description of a presently preferred embodiment, which is illustrated, schematically, in the accompanying drawings.

BRIEF DESCRIPTION OF THE SCHEMATIC DIAGRAM

FIG. 1 is a schematic of the prior art, the two stage AC to DC converter (LLC).

FIG. 2 is a schematic diagram of the present invention.

FIG. 3 is the another arrangement of the present invention

FIG. 4 is yet another arrangement of the present invention

FIG. 5 is yet another arrangement of the present invention.

FIG. 6 is yet another arrangement of the present invention.

FIG. 7 is 120v arrangement of the present invention.

FIG. 8 a and FIG. 8 b are connecting diagrams of the forward transformer winding with two diodes.

FIG. 9 is the input current waveform of 210 w TV power supply(LLC)

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before explaining the disclosed embodiment of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. The topology of the present invention is that a first winding of a forward transformer is connected with a capacitor in series then paralleled with another capacitor and this circuit is connected with primary winding of the main transformer in series as primary load circuit in LLC power supply, the energy through the forward transformer is used to correct input current waveform and the energy through the main transformer is transferred to the secondary circuit.

Refer to FIG. 2 single stage PFC LLC converter including:

A full-bridge rectifier BD10, a inductor L10, four capacitors C10, C12, C14 and C16, two diodes D12 and D10, one forward transformer, one main transformer, two switches Q10,Q12 and a secondary circuit.

The full-bridge rectifier is connected to AC power lines by its input terminals and its output terminal outputs a rectified voltage.

The inductor has two terminals and its first terminal is coupled to the positive output terminal of the rectifier BD10.

The first diode D10 has a cathode and an anode which is coupled to the second terminal of the inductor L10.

The second diode D12 has a cathode and an anode which is coupled to the second terminal of the inductor L10 and the anode of the first diode D10.

The forward transformer T10 has a first winding and a second winding with a central tap, the two end terminals of the second winding are connected to cathodes of diode D10, D12 separately.

The first capacitor C10 is coupled to the outputs of the full-rectifier BD10.

The second capacitor C12 has a positive terminal which is coupled to the central tap of the second winding of the forward transformer and a negative terminal which is coupled to the negative output of the full-bridge rectifier BD10.

The first switch Q10 has a first terminal which is coupled to the positive terminal of the second capacitor C12, a second terminal and a control terminal which is coupled to control LLC control circuit.

The second switch Q12 has first terminal which is coupled to the second terminal of the first switch Q10, a second terminal which is coupled to negative terminal of the second capacitor C12 and a control terminal which is coupled to a LLC control circuit.

The third capacitor C14 is coupled to the first winding of the forward transformer T10 in series.

The fourth capacitor is connected to the series circuit of the third capacitor C14 and first winding of the forward transformer T10 in parallel. One terminal of this circuit coupled to the junction of the first switch Q10 and the second switch Q12.

The main transformer has a primary winding, in which its first terminal is connected to the circuit consist of first winding of the forward transformer T10 and third capacitor C14 and the fourth capacitor C16 and its second terminal is coupled to the negative terminal of the second capacitor C12, and a secondary winding which is coupled to a secondary circuit.

The Operation of the Diagram as Following:

When the first switch is on, a current discharges from the second capacitor C12, through the fourth capacitor C16 to the primary winding of the main transformer T12 and the negative terminal of the second capacitor C12, another current discharges from the second capacitor C12, through the first winding of the forward transformer T10, third capacitor C14 to primary winding of the main transformer T12 and to negative terminal of the second capacitor C12. The energy through the primary winding of the main transformer is transferred to the secondary circuit, the energy through the first winding of the forward transformer T10 is transferred to the second winding of the forward transformer T10, This energy and the input energy force a current charging the second capacitor C12 through the inductor L10, diode D12 or D10, and the second winding of the forward transformer T10 to central tap and to the second capacitor C12. When the first switch is off and the second switch is on, the energy in the fourth capacitor C16 is discharged through the primary winding of the main transformer T12, the energy in the third capacitor c14 is discharged through the first winding of the forward transformer T10 and the primary winding of the main transformer T12.

The energy through the primary winding of the main transformer T12 is transferred to the secondary circuit. The energy through the first winding of the forward transformer is transferred to the second winding of the forward transformer T10 and this energy and the input energy force a current charging the second capacitor C12 through the inductor L10, diode D12 or D10, and the second winding of the forward transformer T10 to central tap and to the second capacitor C12. This arrangement, that uses the fourth capacitor C16 paralleled with circuit of the first winding of the forward transformer connected with third capacitor C14, is to divide current through main transformer into two routes, one is through the fourth capacitor C16 and the other is through first winding of the forward transformer T10 and the third capacitor C14 to prevent large current through first winding of the forward transformer, the current ratio is dependent on the ratio of the capacitance value of the two capacitors, the third capacitor and the fourth capacitor.

There are two arrangements (FIG. 8 a, FIG. b) for connecting the second winding of the forward transformer T10 to the first diode D10 and the second diode D12, one arrangement is two diodes' anodes coupled together and the cathodes coupled to the end terminals of the second winding of the forward transformer T10 separately. The other arrangement is two diodes's cathodes coupled together and the anodes coupled to the end terminals of the second winding of the forward transformer T10 separately. These two arrangements have two terminals for connecting to other components, one terminal is the central tap of the second winding of the forward transformer, the other is junction of the two diodes's anodes or cathodes.

The inductor L10, the second winding of forward transformer T10 connected with first diode D10 and second diode D12, and the second capacitor C12 are connected in series. The connecting order of the inductor L10 and second capacitor C12 and the second winding of the forward transformer T10 with two capacitors can be changed. When the second winding of forward transformer T10 connected with first diode D10 and second diode D12 is placed in position between positive terminal of the full-bridge rectifier BD10 and positive terminal of the capacitor C12, the cathode of the diodes are connected toward the positive terminal of the capacitor C12.

When the second winding of forward transformer T10 connected with first diode D10 and second diode D12 is placed in the position between the negative output terminal of the full-bridge rectifier BD10 and negative terminal of the second capacitor C12, the anodes of the diodes are connected toward the negative terminal of the second capacitor C12. FIG. 3, FIG. 4, FIG. 5, FIG. 6 are examples of these arrangements.

The ratio of second winding of the forward transformer T10 and the first winding of the forward transformer T10 is >4.

The capacitance value of the third capacitor C14 is larger than the capacitance value of the fourth capacitor C16.

FIG. 7 is 120v single stage PFC LLC power supply arrangement.

Refer to FIG. 7

The Operation Principle as Following:

When the input voltage is in positive half cycle, the input voltage and the induced voltage in the second winding of the forward transformer T10 force a current through the diode D101 or D102 and the inductor L10 charging capacitor C13.

When the input voltage is in negative half cycle, the input voltage and the induced voltage in the second winding of the forward transformer T10 force a current through the diode D10 or D12 and the inductor L10 charging capacitor C12. 

What is claimed:
 1. A single stage PFC LLC converter including: A full-bridge rectifier, a inductor, four capacitors, two diodes, one forward transformer, one main transformer, two switches and a secondary circuit; The full-bridge rectifier is connected to AC power lines by its input terminals, and its output terminal outputs a rectified voltage; The inductor has two terminals and its first terminal is coupled to the positive output terminal of the rectifier; The first diode has a cathode and an anode which is coupled to the second terminal of the inductor; The second diode has a cathode and an anode which is coupled to the second terminal of the inductor and the anode of the first diode; The forward transformer has a first winding and a second winding with a central tap, the two end terminals of the second winding are connected to cathodes of first diode and second diode separately; The first capacitor is coupled to the outputs of the full-rectifier; The second capacitor has a positive terminal which is coupled to the central tap of the second winding of the forward transformer and a negative terminal which is coupled to the negative output of the full-bridge rectifier; The first switch has a first terminal which is coupled to the positive terminal of the second capacitor, a second terminal and a control terminal which is coupled to the LLC control circuit; The second switch has first terminal which is coupled to the second terminal of the first switch, a second terminal which is coupled to negative terminal of the second capacitor and a control terminal which is coupled to a LLC control circuit; Main transformer has a primary winding and a secondary winding which is coupled to a secondary circuit, the primary winding has first terminal and a second terminal which is coupled to the negative terminal of the second capacitor; The third capacitor is coupled to the first winding of the forward transformer in series; The fourth capacitor is coupled to the series circuit of the third capacitor and first winding of the forward transformer in parallel, One terminal of this circuit coupled to the junction of the first switch and the second switch, the other terminal is coupled to the primary winding of the main transformer.
 2. A single stage PFC LLC converter in claim 1, wherein said the circuit, that first winding of the forward transformer is coupled to the third capacitor in series, and then in parallel with the fourth capacitor, and then connected to primary winding of the main transformer, is consisted of the load circuit LLC power supply.
 3. A single stage PFC LLC converter in claim 2, wherein said the fourth capacitor is to provide one route for a current to conduct through to the primary winding of the main transformer and to prevent a full load current conducting through the first winding of the forward transformer, wherein said the first winding of the forward transformer and third capacitor provide another route for a current to conduct through to the primary winding of the main transformer and to provide part of the load current conducting through the first winding of the forward transformer.
 4. A single stage PFC LLC converter in claim 2, wherein said the energy through first winding of the forward transformer is transferred to the second winding of the forward transformer to correct the input current waveform, wherein said the energy through primary winding of the main transformer is transferred to the secondary circuit.
 5. A single stage PFC LLC converter in claim 1, wherein said, the second winding of the forward transformer has two ways to couple to the first diode and the second diode; wherein said one way is that anodes of the first diode and the second diode are coupled together and the cathodes of the first diode and the second diode are coupled to the different terminal of the second winding of the forward transformer; wherein said the other way is that cathodes of the first diode and the second diode are coupled together and the anodes of the first diode and the second diode are coupled to the different terminals of the second winding of the forward transformer.
 6. A single stage PFC LLC converter in claim 1, wherein said the second winding of the forward transformer is used to draw a current from the input to the second capacitor.
 7. A single stage PFC LLC converter in claim 1, wherein said the inductor is an energy storage component, it stores energy when there is a voltage force a current through it, it relieves the energy when the voltage is off.
 8. A single stage PFC LLC converter in claim 1, wherein said the inductor, the second capacitor and second winding of the forward transformer with the first diode and the second diode are connected in series, and these components have several connection orders and these different arrangements have the same function.
 9. A 120v single stage PFC LLC converter consisting of: Four diodes: first diode, second diode, third, and fourth diode, Four capacitors: first capacitor, second capacitor, third capacitor and fourth capacitor One inductor One fourth transformer with a first winding and a second winding with a central tap One main transformer with a primary winding and a secondary winding A secondary circuit Two switches: first switch, second switch; The inductor has two terminals, a first terminal is coupled to an input power line; The central tap of the second winding of the forward transformer is coupled to the other input power line; The first capacitor has a positive terminal and negative terminal which is coupled to the second terminal of the inductor; The second capacitor has a positive terminal which is coupled to the second terminal of the inductor and negative terminal of the first capacitor; The first diode has its anode coupled to the first terminal of the second winding of the forward transformer and its cathode coupled to the positive terminal of the first capacitor; The second has its anode coupled to the second terminal of the second winding of the forward transformer and its cathode coupled to the positive terminal of the first capacitor; The third diode has its cathode coupled to the first terminal of the second winding of the forward transformer and its anode coupled to the negative terminal of the second capacitor; The fourth diode has its cathode coupled to the second terminal of the second winding of the forward transformer and its anode coupled to the negative terminal of the second capacitor; The first switch has a first terminal coupled to the positive terminal of the first capacitor, a second terminal and a control terminal coupled to LLC control circuit; The second switch has a first terminal coupled to the second terminal of the first switch, a second terminal coupled to the negative terminal of the second capacitor; a control terminal coupled to the LLC control circuit; The third capacitor has a first terminal coupled to the first terminal of the first winding of the forward transformer and a second terminal, the second terminal of the first winding of the forward transformer coupled to the second terminal of the first switch and the first terminal of the second switch; The fourth capacitor has a first terminal coupled to the second terminal of the first winding of the forward transformer and a second terminal coupled to the second terminal of the third capacitor; The primary winding of the main transformer has a first terminal coupled to the second terminals of the third capacitor and the fourth capacitor and a second terminal of primary winding coupled to the negative terminal of the second capacitor, the secondary winding of the main transformer is coupled to the secondary circuit.
 10. A 120v single stage PFC LLC converter in claim 9, wherein said first winding of the forward transformer is used to transfer energy to the second winding of the forward transformer to correct input current waveform.
 11. A 120v single stage PFC LLC converter in claim 9, wherein said the inductor is energy storage component, it stores energy when there is a voltage that forces a current through it, it relieves the energy when the voltage is off.
 12. A 120v single stage PFC LLC converter in claim 9, wherein said there are two way to connect an inductor to the circuit, one way is that the inductor is connected to central tap of the second winding of the forward transformer and the other is that the inductor is connected to junction of the first capacitor and the second capacitor.
 13. A 120v single stage PFC LLC converter in claim 9, wherein said the first diode and the second diode is used to draw current to the first capacitor, when input voltage is in the positive half cycle, and where said the third and fourth diode is used to draw the current to the second capacitor when the input voltage is in negative half cycle.
 14. A 120v single stage PFC LLC converter in claim 9, wherein said the second winding is used to provide energy to draw a current from input to first capacitor and the second capacitor 